Fluorinated elastomeric materials (sometimes referred to hereinafter either as fluorinated elastomers or fluoroelastomers) are synthetic, noncrystalline polymers which are usually vulcanized or cured to enhance their properties for use in a variety of industrial articles, such as molded or shaped parts. See for example Grootaert, W. M., Millet, G. H. and Worm, A. T., "Fluorocarbon Elastomers", Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 8, pp. 990-1005, 4th ed., John Wiley & Sons, 1993. Typically they are used in the more demanding applications where exposure to extreme heat or harsh chemical or solvent environments is encountered.
Processes used for making molded fluoroelastomer articles, for example O-rings, inherently have a relatively high degree of waste, e.g., 30% or higher. This waste, also commonly called scrap, may include flash, sprue and runners, and out-of specification parts.
It is desirable to reuse (i.e., recycle) this waste material. However, for a variety of reasons, it has been very difficult to do so. For example, the waste material cannot be recycled merely by grinding and reforming as with many thermoplastic polymer operations. Usually such direct addition of the waste material results in a composition having a higher minimum viscosity. This increase in minimum viscosity typically negatively affects later processes, such as injection molding.
It has also been generally observed that the inclusion of waste material in a fluoroelastomer formulation has a negative effect on both the cure rheology and the physical properties of articles made from such formulations. Both are inferior to those demonstrated by formulations, and the resultant articles, that do not contain waste material (i.e., virgin formulations and articles).
The cure rheology of a formulation containing scrap may be deficient in several ways. For example, the cure rheology generally exhibits a reduction in scorch time, an increase in the cure time, and a lessening of final crosslink density. As a result, formulations containing scrap begin the onset of cure more quickly (scorch) and either take an unacceptable amount of time to reach the desired level of cure or crosslink density, or fail to reach the desired cure or crosslink density. These effects are undesirable.
The use of waste material also typically negatively affects the physical properties of the completed articles. For example, resistance to compression set is reduced. This is undesirable when, for example, the finished article, such as an O-ring or a gasket, will be used to form a seal. Such applications typically require a high resistance to compression set.